String for a spring?

[GHA]

Do you think this bit of string will be OK as a spring for a 10t boat? Was 5mm but seems to have shrunk down the more like 4mm.

Might be ok but just seems a bit small....

 

[johnalison]

It'll be absolutely fine until it breaks.

 

[GHA]

It'll be absolutely fine until it breaks.

Which will be round about the weight of a ford transit van.

Just a little test to see how dyneema stands up to abrasion. In this case 5mm d12 SK99 dyneema. It's a short strop into an eye with 16mm 3 strand nylon into that with a bow line. Much quieter onboard without the creaking stretch of the 3 strand. Nylon is new and has a MBS of 5T, so probably slightly weaker than the dyneema with the loss of strength in the bowline. Dyneema splices should be not far off 100% , mid nineties anyway. (done properly with tapered buries).

DIAMETER
AVERAGE BREAK LOAD(kg)
WEIGHT (kg/100m)

[TH="align: center"]2.5mm[/TH]
[TH="align: center"]3mm[/TH]
[TH="align: center"]3.5mm[/TH]
[TH="align: center"]4mm[/TH]
[TH="align: center"]5mm[/TH]
[TH="align: center"]6mm[/TH]
[TH="align: center"]7mm[/TH]
[TH="align: center"]8mm[/TH]
[TH="align: center"]9mm[/TH]
[TH="align: center"]10mm[/TH]
[TH="align: center"]11mm[/TH]
[TH="align: center"]13mm[/TH]
[TH="align: center"]15mm[/TH]
[TH="align: center"]16mm[/TH]
[TH="align: center"]18mm[/TH]
[TH="align: center"]20mm[/TH]

[TD="align: center"]677[/TD]
[TD="align: center"]1184[/TD]
[TD="align: center"]1706[/TD]
[TD="align: center"]2447[/TD]
[TD="align: center"]2804[/TD]
[TD="align: center"]4150[/TD]
[TD="align: center"]6378[/TD]
[TD="align: center"]7533[/TD]
[TD="align: center"]8259[/TD]
[TD="align: center"]11036[/TD]
[TD="align: center"]13794[/TD]
[TD="align: center"]18387[/TD]
[TD="align: center"]21365[/TD]
[TD="align: center"]24475[/TD]
[TD="align: center"]29174[/TD]
[TD="align: center"]38883[/TD]

[TD="align: center"]0.37[/TD]
[TD="align: center"]0.53[/TD]
[TD="align: center"]0.74[/TD]
[TD="align: center"]0.98[/TD]
[TD="align: center"]1.28[/TD]
[TD="align: center"]1.77[/TD]
[TD="align: center"]2.80[/TD]
[TD="align: center"]3.30[/TD]
[TD="align: center"]3.76[/TD]
[TD="align: center"]4.83[/TD]
[TD="align: center"]5.82[/TD]
[TD="align: center"]8.00[/TD]
[TD="align: center"]9.80[/TD]
[TD="align: center"]11.80[/TD]
[TD="align: center"]14.30[/TD]
[TD="align: center"]18.00[/TD]

So guesses how long before I chicken out if the abrasion gets too much.

I reckon quite some time.....

 

[NormanS]

I would have thought that you would want some stretch.

 

[GHA]

I would have thought that you would want some stretch.

Most of the spring is nylon.

 

[NormanS]

Most of the spring is nylon.

Ah, so you're only giving us half the story.

 

[GHA]

Ah, so you're only giving us half the story.

Only first post, have a look at 3..

It's a short strop into an eye with 16mm 3 strand nylon into that with a bow line.

..Maybe not perfectly cleat, but theres a short piece of d12 dyneema terminating in a eye just clear of the bow fairlead, into that goes a piece of 16mm nylon other end of which goes onto the pontoon cleat.

Object of the exercise is, just out of interest , see how well dyneema can cope with chafe. Boat is in Dartmouth which quite often can get some swell in so the strop is working seriously hard a lot of the time.

I reckon it will stand up to the punishment.

We'll see

 

[johnalison]

As you say, it's the chafe or otherwise which will decide rather than the theoretical strength.

 

[GHA]

I got the wrong dataset before, 5mm actually 3.8T max breaking load, with

• "Marlow ArmourCoat, increases the life of the rope by reducing UV and abrasion fatigue."

So I suspect it will last for ages.
Incredible material.
http://www.marlowropes.com/leisure-marine-products-1/grand-prix-series/d12-max-90.html

 

[Neeves]

I think you must know that Evans has done a lot of work on the abrasion resistance of dyneema (as you referenced his website on sewing 'splices'), why not just look at his work on use of dyneema for his snubbers.



Jonathan

 

[Thistle]

So I suspect it will last for ages.
Incredible material.

You're probably right but what are the downsides for your boat and those around if you're wrong? If you are doing this primarily as a test, have you thought of putting in another slightly slacker line as a backup?

 

[GHA]

You're probably right but what are the downsides for your boat and those around if you're wrong? If you are doing this primarily as a test, have you thought of putting in another slightly slacker line as a backup?

Living aboard it gets checked many times every day

And would never leave the boat for any length of time without backups even if using normal line.

 

[GHA]

I think you must know that Evans has done a lot of work on the abrasion resistance of dyneema (as you referenced his website on sewing 'splices'), why not just look at his work on use of dyneema for his snubbers.



Jonathan

I have the load testing downloaded which has a good bit on dyneema but haven't found any specific to snubber abrasion - any links? Anyway, different dyneema. Nothing like the real world to see what goes on in the real world.

 

[Neeves]

No links - but I do know Evans has done a lot of work on snubbers and dyneema, I hate to mention it but 'anchor snubbers'. He was using climbing rope with a dyneema tail, the latter only for abrasion. But he had dropped climbing rope in favour of (something else - nylon?) for the simply reason climbing rope was impossible to splice. He has been using it - in the real world. Thinwater would know much more about it than I, as he and Evans had common interests, we'll have to hope Thinwater has thick skin

Evans was happy with climbing rope - other than the inability to splice. We use (have been for 3 years now( climbing rope, as a snubber (in the real world) but have no abrasion issues.

Jonathan

 

[vyv_cox]

Your figures for 5 mm Dyneema load at break are far higher than I measured last week. A range of ropes from different manufacturers all broke at near enough 2 tons for SK75 and SK78.

 

[Neeves]

Sorry - too focussed on one specific issue.

We have been using hollow dyneema braid, like the outer cover of any braid on braid, made from dyneema as an abrasion resistant cover. Works a treat - in the real world. We got ours from Nautilus Braids in NZ but there must be UK, or European, producers. You sew on at one end of the item you want to protect and leave the other end free - to allow the inner core to stretch. I imagine you can obtain any diameter but ours was a nominal 10mm hollow tape but by bunching it up (loosening the braid) we inserted 11mm cord.

We use the same follow braid with our sheets, both genoa and screacher, inserted inside, one sheet at each end and leave the centre empty (sewn with braided, dyneema fishing line). We then cow hitch - the hitch is low profile, so does not catch on anything and resists abrasion. Joining sheets with tubular tape is not new - we used to do it when racing 30 years ago - dyneema has allowed a much longer life.

Testing ensures that you do not make stupid mistake - easy with novel materials or applications

All tested (to check sewing thread etc) and then used - in the real world, which is as it should be

Jonathan

 

[GHA]

Your figures for 5 mm Dyneema load at break are far higher than I measured last week. A range of ropes from different manufacturers all broke at near enough 2 tons for SK75 and SK78.

Interesting, sounds a bit low - how were you terminating it?

If broke some 5mm from New England ropes a while ago, it went around 2200Kg from memory, but that was with a straight cut tail in a bury splice, not tapered. It went right at the end of the buried tail. Tapered tails are much closer to max breaking strain apparently, which was around 2800Kg for that rope.


The stuff I'm using is D12 MAX SK99, probably as high spec as you can get at the moment. I'll stick some in the post if you like, I got a load of it used once off a job so didn't buy it

 

[dunedin]

A very thin rope under high strain and a lot of movement .............. will probably do a fair amount of damage to any bits of boat that it comes up against. A good impression on a hacksaw blade

 

[vyv_cox]

All test pieces were spliced back into loops at each end. The 2 tons figure was consistent although one supplier queried it as they were expecting 2.2 tons.

 

[reeac]

Do you think this bit of string will be OK as a spring for a 10t boat? Was 5mm but seems to have shrunk down the more like 4mm.

Might be ok but just seems a bit small....

I used a length of Dyneema to connect a steel centre plate to a windlass. Left the boat on a swinging mooring for less than a week with the plate just slightly raised to reduce rocking on the pivot. The covering of the Dyneema was worn through where it passed over a smooth Iroko surface by the time I next visited the boat. Replaced it with s/s wire.